Sorry if I am ranting a bit here, but it happens at times when I start writing. And I hope I don't come off as confrontational towards you it is not my intention.
>Someone on a bad day sees you and doesn't like the look of your face.
This could easily be someone who would stab you or run you over with his car or whatever. You can't guard you against all eventualities no matter what.
>[…] so the situation doesn't escalate because of misunderstandings
This would be down to training and reading people. Usually when you take out a threat you keep your gun trained at the threat in case you need to neutralize it some more. Someone on an rampage would not keep their gun trained on a single individual or individuals that are already neutralized. Someone on an rampage would seek out their next target. But again you can never safeguard against all eventualities. Also you need to keep in mind that when you are rushing into a gunfight you need to assess the situation because you don't know what caused it. Running towards a gunfight is different than reacting to someone pulling a gun. Keeping a level head is alpha and omega in every situation.
But I think the scenario with automatic rifles is taking it a bit far as no one has automatic rifles (at most they are semi-automatic), and conceal carry of a rifle is a feat in itself. Most likely the massacre would never happen there because he would see that there were at least three people with rifles ready at hand. The disturbed man would probably seek out a no-gun zone and kill innocent people in a safe environment.
But I get what you are trying to say, and yes misunderstandings could escalate things. But I doubt there would be an uncontrolled chain reaction where people starting shooting each other left and right. I think worst case there would be one or two accidental deaths perhaps in your scenario.
>I mean that most criminals are too dumb or insane to consider the consequences of their actions
One could hope that in time these people would be Darwined out of existence if they were shot before they were able to procreate, but it would take some generations to get to that point.
>I definitely don't wish for Europe to end up the same way
You know there is two acid attacks every day in Britain? Britain have become the country with most acid attacks per inhabitant in the world. So it is not like Europe is without its problems when it comes to violence. Violent people will always find a way, be it by car, hammer or wooden stick. Also criminals will always be able to get guns if they want to. As you say they don't think of the consequences so they will not be deterred by the fact that they might get caught when they try to buy a gun illegally. Upstanding citizens on the other hand will not try to get guns illegally, but they might want to get one legally if they were given the opportunity. So raising the bar for getting guns, or out right banning, only keeps guns out of the hands of those who would not use the guns for bad things. http://archive.is/rDl3j
Also there is no real correlation between gun-ownership per capita and gun-violence per capita.https://en.wikipedia.org/wiki/List_of_countries_by_firearm-related_death_rate
Someone with better statistical knowledge and infographs and such can probably point this out better; like if you remove suicides and adjust the numbers to adjust for guns per capita. I think if you look at statistics you will see that there is a greater correlation between "We wuz kangs" and gun violence than ownership per capita.
One thing I think we could say for sure is that if there was more guns in the Nordic countries there would be many more suicides by guns here. We are already pretty high on the suicide statistics already; Finland is in 4th place, and Norway in 13th place already (not adjusted for guns per capita). Heck all the Nordic countries are within the first 21th places when it comes to suicide by gun.